Subsea transportation of oil, gas and water will generally be carried out by means of separate pipes for different media. In connection with multiphase production from a subsea well to a platform or land based installation, the flow from the well may comprise oil, gas and water in a mixture.
During subsea transportation the pipes and the contents thereof may be cooled to a subsea temperature of 3.degree. C.
In connection with the transportation of unstabilized oil, this cooling may involve increased viscosity and/or deposits of wax on the cooled pipe surface that can lead to blocking of the flow.
Correspondingly, a super-cooled multiphase flow can during high pressure develop hydrate formations which may block the pipeline and cause time consuming and costly cleaning work.
Due to this reason temperature sensitive pipes will be insulated and are often supplied with chemicals which hampers the deposit and the formation of hydrates. An alternative is to employ electrical heating of thermally insulated pipes, such that the temperature is usually kept above 20.degree. C.
The laying of separate process pipes for production as well as gas and water injection, etc., represents a substantial expenditure as regards the laying, burying and installation in the proximity of the platform.
A simplified method for such work is to collect the process pipes in a so-called pipe or pipeline bundle, wherein the pipelines are kept at a mutual spacing.
In order to, inter alia, strengthen the supporting properties of the structure, render protection to the process pipes, simplify the laying, etc., the pipe bundle is often mounted in a surrounding outer carrier pipe with appropriate properties.
In connection with temperature sensitive process pipes it is known that process pipes having preheated injection water, alternatively a dedicated pipe loop carrying preheated medium, can be used for heating such pipe bundles. The pipe bundle must then have an outer thermal insulation and be filled with liquid and/or gas for the distribution and transfer of heat.
Such heating is clearly limited as regards the transportation in long pipes of liquid require a sufficiently high temperature along the overall length of said pipes.